A technique known as OpenFlow has been proposed in Patent Literatures 1 to 3 and in Non-Patent Literatures 1, 2. The OpenFlow comprehends communication as an end-to-end flow and manages path control, recovery from malfunctions, load balancing and optimization on the flow-by-flow basis. An OpenFlow switch, specified in Non-Patent Literature 2, includes a secure channel over which to communicate with an OpenFlow controller, and operates in accordance with a flow table an addition to or a rewriting in which is instructed from time to time from the OpenFlow controller. In the flow table, a set of match conditions (Match Fields) to be matched against a packet header, flow statistics information (Counters) and instructions that define the processing contents (Instructions) is defined from one flow to the next. See ‘5.2 Flow Table’ of Non-Patent Literature 2.
On receipt of a packet, the OpenFlow switch searches from the flow table an entry having the match condition conforming to the header information of the received packet. See ‘5.3 Matching’ of Non-Patent Literature 2. If, as a result of the search, the entry matched to the received packet is found, the OpenFlow switch updates the flow statistics information (Counter), at the same time as it executes processing contents stated in an instruction field of the matched entry, such as packet transmission at a specified port, flooding or dropping. If conversely no entry matched to the received packet is found, the OpenFlow switch sends an entry setting request, that is, a request for transmission of the control information to process the control information (Packet-In message), to the OpenFlow controller over the secure channel. The OpenFlow switch receives the flow entry, in which processing contents are stated, and updates the flow table. In this manner, the OpenFlow switch uses the entry, stored in the flow table, as the control information, in order to forward the packet.